Mobility of major-, minor- and trace elements in solutions of a planosolic soil: distribution and controlling factors

Subsurface waters circulating in an unpolluted soil of a planosolic horizon (Massif Central, France) were studied in order to determine their physico-chemical characteristics. Three water sampling sites were chosen along a toposequence according to topography. For each site, two piezometers were placed above and in the gravely and concretion-rich horizon (Feand Mnoxyhydroxides). Concentrations of major-, minor(cations, anions, iron, manganese, phosphorus, silica) and trace elements (Al, Cd, Co, Cr, Cu, Ni, Pb, Zn, U) were monitored on bulk and filtered water (0.45 μm) to study both the particulate and the dissolved components, from 2004 to 2006, during the soil saturation period (i.e. from November to May). Chemical characteristics of soil solutions provide evidence for various chemical water compositions and for time variations of the water quality, pointing out that the hydrodynamic and chemical reactivity in the solution is different for the three sites. Calculations of pe values allow to give an information about a range of the redox state of soil solutions. The pe ranges are different for each piezometer but correspond to anoxic solution. For all piezometers, distribution between the dissolved and the particulate fraction and correlations between the various elements in the soil solutions indicate that: (i) Al and Fe show similar behaviour, (ii) Al is mainly present as oxyhydroxides and (iii) some trace metals are mainly associated with particles which * Corresponding author E-mail address: [email protected] (A. Pelfrêne) in su -0 04 09 65 0, v er si on 1 7 Se p 20 09 Author manuscript, published in "Applied Geochemistry 24, 1 (2009) 96-105" DOI : 10.1016/j.apgeochem.2008.11.006